1. Field of the Invention
The present invention relates to an apparatus and method for estimating a distance by using time of arrival (TOA), and more particularly, to an apparatus and method for simply and quickly detecting a distance between wireless devices employed in a wireless location awareness system by detecting TOA using a single counter.
2. Description of the Related Art
In general, wireless location awareness systems employ methods of estimating a present location via wireless communication with other wireless communication devices using a wireless signal. Location information obtained by location awareness systems is importantly used when efficiently using information obtained by wireless communication via more efficient network construction.
To improve accuracy of location awareness in wireless location awareness systems, it is very important to accurately detect a distance between two wireless communication devices. Generally, to estimate a distance between two wireless communication devices, the distance is calculated by detecting time of arrival (TOA) that is an amount of time used in transmitting and receiving a signal in wireless communication between the two wireless communication devices. Also, pulses are count by using a counter and a count value of the pulses and frequencies of the pulses are used, thereby detecting the TOA.
FIGS. 1 and 2 are timing diagrams illustrating a conventional method of detecting TOA. Referring to FIGS. 1 and 2, there are shown pulses used to estimate a distance between a first wireless communication device (not shown) and a second wireless communication device (not shown) and count timing. Generally, the first wireless communication device transmits a ranging signal to the second wireless communication device, the second wireless communication device transmits a response signal to the first wireless communication device in response to the ranging signal, and the distance is detected by calculating an amount of time between a point in time of transmitting the ranging signal and a point in time of receiving the response signal.
The first wireless communication device transmits the ranging signal to the second wireless communication device at a time point t0 simultaneously with generating a reference pulse P0 with a predetermined frequency f0 and counts the reference pulses P0. The second wireless communication device receiving the ranging signal transmits the response signal responding to the ranging signal to the first wireless communication device. The first wireless communication device receives the response signal at a time point t1 simultaneously with generating a delay pulse P1 having a different frequency f1 from the frequency f0 of the reference pulse and counts the delay pulse P1. Also, the first wireless communication device detects and counts an overlap of the reference pulse P0 and the delay pulse P1. A time point t2 is a point in time that the reference pulse P0 and the delay pulse P1 start to overlap with each other, and a time point t3 is a point in time the overlap is finished.
In this case, there are generated three count values such as a count value N1 of the reference pulse P0, a count value N2 of the delay pulse P1, and an overlap count value N3. In general, as shown in Equation 1, a round-trip time Tx of the signal transmitted between the first wireless communication device and the second wireless communication device by using the three count values.
                                          t            ′                    =                                                                      (                                                            N                      ⁢                                                                                          ⁢                      1                                        +                                                                  N                        ⁢                                                                                                  ⁢                        3                                            2                                                        )                                /                f                            ⁢                                                          ⁢              0                        =                                          T                ⁢                                                                  ⁢                x                            +                                                                    (                                                                  N                        ⁢                                                                                                  ⁢                        2                                            +                                                                        N                          ⁢                                                                                                          ⁢                          3                                                2                                                              )                                    /                  f                                ⁢                                                                  ⁢                1                                                    ⁢                                  ⁢                              T            ⁢                                                  ⁢            x                    =                                                                      (                                                            N                      ⁢                                                                                          ⁢                      1                                        +                                                                  N                        ⁢                                                                                                  ⁢                        3                                            2                                                        )                                /                f                            ⁢                                                          ⁢              0                        -                                                            (                                                            N                      ⁢                                                                                          ⁢                      2                                        +                                                                  N                        ⁢                                                                                                  ⁢                        3                                            2                                                        )                                /                f                            ⁢                                                          ⁢              1                                                          Equation        ⁢                                  ⁢        1            
Where t′ is a time point of a middle in a section where an overlap is detected.
The distance between the two wireless communication devices may be estimated by using a round-trip time calculated using Equation 1.
However, to apply conventional ranging methods, three counters for detecting three count values N1 to N3 are required, thereby increasing complexity of wireless communication devices.
Also, in conventional ranging method, it is required to detect sections where a reference pulse and a delay pulse overlap with each other. When pulses are a high frequency, it may be possible that an overlapped portion is not detected or a wrong portion is detected due to performance of a detector detecting an overlap or an internal glitch.
In addition, an amount of time for ranging is increased to detect overall sections where the reference pulse and the delay pulse overlap with each other.